Samsung T240 No power. No Power Led turning on

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

Update :

I desoldered the IC101 & in the process destroyed the legs of it. Managed to read the marking on it using a microscope, albeit the difficulty, and Jet is right. It is marked FAN7602 although the marking is a bit difficult to see.

I managed to get 2 pieces of FAN7602C from a local store. I also bought 2 pieces of Mosfet 7N65C just in case. Replaced the FAN7602C only and monitor works well for 2-3 hours. Voltage across the startup cap, I remembered measuring, was 11-12V stable and all the secondary voltages were there. I kept it on standby overnight and when the next morning comes, the monitor is behaving as it originally came (No power LED). Sigh! I dissembled again and this time I measured that voltage across the startup cap is now 35V?!

Do you think the newly replaced IC101 FAN7602C is faulty again? Any other opinions?

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

I dissembled again and this time I measured that voltage across the startup cap is now 35V?!

35V is way too high. The IC101 can only take 20V maximum according to the datasheet. The IC101 is now in OVP (over-voltage protection). It shuts down when VCC reaches 19V.

Do you think the newly replaced IC101 FAN7602C is faulty again? Any other opinions?

1) You never did answer if D103 was shorted out of circuit or not. You may want to recheck all your diodes in case one is shorted.

2) Check your soldering on IC101.

3) See if C02, C10, C11 (by IC101) are shorted or possibly damaged from your soldering.

[retiredcaps]

Re: Samsung T240 No power. No Power Led turning on

and Jet is right.

Was there any doubt?

[selldoor]

Re: Samsung T240 No power. No Power Led turning on

I measured that voltage across the startup cap is now 35V?!

You did have your meter on vDC?

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

35V is way too high. The IC101 can only take 20V maximum according to the datasheet. The IC101 is now in OVP (over-voltage protection). It shuts down when VCC reaches 19V.
1) You never did answer if D103 was shorted out of circuit or not. You may want to recheck all your diodes in case one is shorted.

2) Check your soldering on IC101.

3) See if C02, C10, C11 (by IC101) are shorted or possibly damaged from your soldering.

Agree with you. But i am confused what makes it jumps so high now.

1) .. Sorry. Age is catching up.. heez.
D103 (OOC) reads (on diode option) 664 and out of range when probe is reversed.

2) Done it. But could not see any shorting. Verified by using the multimeter resistance option as well

3) Visual check observed they are not destroyed. Measurement in diode option reads
C02 - 570, out of range
C10 - 645, 1097
C11 - 787, out of range
Hopefully they are fine because i have no way to tell what their capacitance value are.

Was there any doubt?

as usual.... ..

You did have your meter on vDC?

Yes sir!.. was turned to DC..

Just to note that i have bought another spare IC101 (FAN7602).. worth a try to replace it again?. Or do you guys think that it is a waste of time to do so..

[jetadm123]

Re: Samsung T240 No power. No Power Led turning on

I had to do a little homework on this one. Apparently, there are 2 versions of the FAN7602, FAN7602B and FAN7602C. FAN7602B has a fixed switching frequency of 65kHz, while the FAN7602C is not fixed. I believe you should be using the FAN7602B, since many of the power supplies use a fixed frequency controller chip.

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

Jet, appreciate your time & effort. I believe this should be the one that i have to order. If that is the case, then looks like this project need to be stored in the 'freezer' for 2-3 weeks till the parts becomes available.

[haresh21]

Re: Samsung T240 No power. No Power Led turning on

change the optocoupler with TL431 transister i sure. and repair this.

[newbie1]

Re: Samsung T240 No power. No Power Led turning on

Hey guys.
Just to update that i did not yet buy the FAN7602B as suggested. I decided to replace the MOSFET 7n65c first before purchasing them. Upon further close-up inspection, i saw a dead tiny insect caught in between the back of the drain pin of the Mosfet to the heatsink. I am not sure whether that is the cause of the failure, but once i replaced the Mosfet the monitor works fine. I have stable 12v across the startup cap and it has been running for a few days without any hiccups... yet.

My thanks to the usual reliable 'gurus'.. Jetadm, Retiredcaps, Selldoor & Rtech..